Evidence has been building since the early 2010s that rats with significant debilitating spinal injuries can regain control of paralyzed limbs through a combination of robot-assisted rehabilitation and electrochemical spinal cord stimulation.

The research is bringing new hope to spinal cord injury sufferers and giving rise to technologies that could one day assist in developing an effective treatment for many forms of spinal cord injury.

Back in early 2014, I covered the grueling recovery efforts of Mark Pollock, a blind, paralyzed endurance athlete who's been using a combination of electrochemical stimulation and robotic rehab since falling from an open window and breaking his back. At the time I wrote the story, the promise of the treatments seemed almost magical, in part because no one could satisfactorily explain why or how they worked in trials with rats.

Until now.

Researchers with the National Centre of Competence in Research (NCCR) Robotics, a Swiss organization that pulls together top researchers to aid in development of human-oriented robotics, have, for the first time, observed how the brains of rats receiving therapeutic treatments are able to reroute task-specific motor commands through alternative neural pathways.

"The brain develops new anatomical connections through regions of the nervous system that are still intact after injury," says NCCR Robotics Professor Grégoire Courtine. "The brain essentially rewires circuits from the cerebral cortex, brainstem and spinal cord--an extensive rewiring that we exposed to unprecedented detail using next-generation whole brain-spinal cord microscopy."

Lead author Léonie Asboth, a scientist with the École polytechnique fédérale de Lausanne, a participating research university in Lausanne, Switzerland, explains that robotic rehab therapy, in which a robotic mechanism moves a subject through a series of motions, is essential to that rewiring process.

"The recovery is not spontaneous," says Asboth. "You need to engage the animals in an intense rehabilitation therapy for the rewiring to take place. In our case, this therapy involves electrochemical stimulation of the spinal cord and active physiotherapy in a smart assistive harness."

Companies like Ekso Bionics and ReWalk, which make robotic suits used in physical therapy, including with spinal cord injury sufferers, have been touting the promising research.

In the NCCR lab, rats whose spinal cords have been surgically severed are treated first with pharmaceuticals and then with electricity to stimulate the spinal cord and activate muscles below the injury.

The pharmaceutical and chemical treatment is combined with therapy in a smart harness, which takes the weight of the rats off the legs places them in natural walking positions.

After a very short period of time--as quickly as a few weeks--the rats regain extensive control over their hind limbs and can walk on their own without any stimulation or external aid.

The Swiss researchers compared the brains of injured rats after rehabilitation to the brains of healthy rats using a light-sheet microscope, which creates a 3D image of neural tracts in the removed rat brains.

The images show how the therapy reorganizes these pathways. Crucially, the injured neurons do not regrow.

"A reorganization of the neural branching occurs above the injury," according to an NCCR spokesperson, "leading to new connections."

So-called neuroprosthetic rehabilitation has not been conclusively studied on people. But the Swiss researchers are optimistic.

"We previously showed that plasticity, the remarkable ability of the nervous system to grow new connections after spinal cord injury, is even more robust in humans than in rodents," says Courtine. "We are currently testing our therapy in people with spinal cord injury at the Lausanne university hospital (CHUV)."

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